1. Field of the Invention
2. Description of Related Art
The invention relates to an X-ray device which includes an X-ray tube provided with means for influencing the electron flow through the X-ray tube. The invention also relates to a piezoelectric transformer which includes at least two piezoelectric elements.
The tube current in X-ray tubes can be directly switched off, and hence also the X-rays, by means of a grid which can be connected to a negative grid voltage relative to the cathode potential. Consequently, the X-ray tube can operate with a constant high voltage and no undesirable soft X-rays, are produced which would affect the patient and the attending staff. The grid is driven at the high voltage potential of the cathode which may amount to, for example -75 kV with respect to ground. The voltages required for the reverse and forward modes of the X-ray tube are generated by means of complex electronic grid control circuitry. An X-ray tube of this kind is known from DE-OS 20 07 246.
Using an electrostatic deflection device, the electrons emitted by the cathode in an X-ray tube can be deflected so as to enable variation of the point of incidence (focus) of the electrons on the anode. An X-ray tube of this kind, in which the control voltages for the electrostatic deflection device are generated by means of complex electronic circuitry, is known from EP-B1-480 796.
Piezoelectric transformers are known electric components which utilize the direct piezoelectric effect and at the same time its reversal in a component. Electric energy is first converted into mechanical energy in a first piezoelectric element and, after the internal transfer of mechanical energy from the first to a second piezoelectric element, it is converted into electric energy again in the second piezoelectric element. The voltage transformer used is a piezoelectric type which, for example, steps up a low voltage applied to its input to a high voltage at its output. A piezoelectric transformer may have a very high transformation ratio in such a case.
Often a problem is encountered that a signal must be transformed and that at the same time the signal (to be transformed) has a potential other than that of the (transformed) output signal. Therefore, often steps are required for potential separation between the input signal and the output signal.